1. Field of the Invention
This invention relates to a hot-melt ink composition used in ink-jet recording apparatus. More particularly, it relates to a hot-melt ink composition used when ink is heated to melt under conditions of a higher temperature than room temperature to make a record.
2. Description of the Related Art
As ink-jet recording systems, various systems have been proposed, e.g., what is called an electric field control system, in which electrostatic attraction is utilized to eject ink; what is called a drop on-demand system (or pressure pulse system), in which vibratory pressure of a piezoelectric device is utilized to eject ink; and what is called a thermal ink-jet system, in which a pressure produced by bubbles formed and grown by high heat is utilized to eject ink. These systems can provide very highly precise printed images.
In these ink-jet recording systems, water-based inks employing water as a main solvent and oil-based inks employing an organic solvent as a main solvent are commonly used. Printed images obtained using the water-based inks have a poor water resistance in general. On the other hand, the use of oil-based inks can provide printed images having a good water resistance.
However, these water-based inks and oil-based inks are liquid at room temperature, and hence have had disadvantages that feathering tends to occur when images are printed on recording paper and that no sufficient print density can be obtained. Also, because the inks are liquid, they tend to cause formation of deposits to cause a great lowering of the reliability of ink-jet recording systems.
In order to overcome such disadvantages of the conventional inks of a solution type, what is called hot-melt oil-based ink-jet recording ink compositions, which are solid at room temperature and melt upon heating, are proposed. Stated specifically, U.S. Pat. No. 3,653,932 discloses an ink containing a dialkyl sebacate. U.S. Pat. No. 4,390,369 and Japanese Patent Application Laid-open No. 58-108271 disclose an ink containing a natural wax. Japanese Patent Application Laid-open No. 59-22973 discloses an ink containing a stearic acid. Japanese Patent Application Laid-open No. 61-83268 discloses an ink containing an acid or alcohol having 20 to 24 carbon atoms and a ketone having a relatively higher melting point than these. Japanese Patent Application Laid-open No. 62-48774 discloses an ink containing a thermosetting resin having a high hydroxyl value, a solid organic solvent having a melting point lower than 150.degree. C. and a small quantity of a dye substance. Japanese Patent Application Laid-open No. 2-167373 discloses an ink comprised of a colorant, a first solvent which is solid at room temperature and capable of liquefying upon heating to a temperature higher than the room temperature and a second solvent capable of dissolving the first solvent, being liquid at room temperature and being highly volatile. Also, Japanese Patent Application Laid-open No. 62-295973 discloses an ink containing a synthetic wax having a polar group and a dye soluble in the wax.
Japanese Patent Application Laid-open No. 2-29471 discloses an ink comprised of a ketone, an amide wax, a wax and a colorant.
However, none of these hot-melt ink compositions have well satisfied fundamental performances required in inks (stated specifically, ink transparency, color deterioration during storage, etc.) and good print quality. In particular, those having transparency and adhesive properties good enough to be usable for OHPs (overhead projectors) and those which can concurrently prohibit color changes during use have not been available.